The present invention relates to a serial printer for printing and, in particular, to a serial printer which prints the first line of a recording sheet.
When printing on a recording sheet in a serial printer, not only must the recording sheet be inserted along the platen, but the print operation must also be done from the top end of the recording sheet. More specifically, a serial printer has a sheet discharge section on the downstream side of a position of a sheet forward path thereof, the position confronting both the recording head and the platen. The sheet discharge section has sheet discharge ribs and sheet discharge rollers. The sheet discharge section not only assists the recording sheet to be maintained in a predetermined position with respect to the platen for printing, irrespective of the rigidity of the recording sheet, but also discharges the printed recording sheet.
However, in a portion of the sheet forward path, where the top end of the recording sheet reaches the sheet discharge section, the recording sheet projects toward the recording head due to the rigidity thereof. As the sheet continues to move forward while so projected, the top end of the recording sheet lifts up and abuts against the sheet discharge section. The projection of the recording sheet causes a paper jam in the printer. To overcome this problem, various recording sheet insertion techniques have been proposed.
For example, as disclosed in Unexamined Japanese Patent Publication No. Sho. 56-144983, the carriage is brought to the center of the platen and the recording sheet is fed upon operation of a sheet insertion key. In addition, the paper bail is opened. Based on this arrangement, the following operation occurs: (1) the centering of carriage is ended before the recording sheet reaches the paper bail, (2) the paper bail is closed to the original position when the recording sheet is inserted between the paper bail and the platen, and (3) the recording sheet feed operation is stopped. The carriage is thereafter reset to the home position to start printing.
Based on this operation, the center of the recording sheet can be guided by the carriage, which to some extent prevents jamming of sheets. However, one problem with this arrangement is that after the sheet insertion key is operated, the carriage is moved to the center in order to move the recording sheet guide position. This operation takes additional time and affects the timing and reliability of the sheet insertion key operation. There are other problems. First, the printer becomes costly because the paper bail and the mechanism for opening and closing the paper bail are required. Second, the top margin must be set to a large value, because a recording sheet zone between the paper bail and the recording head cannot be printed. Third, a high performance control means and a large capacity power supply are required because the operations of centering the carriage, feeding the recording sheet, opening and closing the paper bail, and a like operation are performed simultaneously. In addition, a high performance controller and a large capacity power supply are required. Such factors also elevate the cost of manufacture.
To overcome the above-noted problems, a number of printers have been proposed. For example, as disclosed in Unexamined Japanese Patent Publication No. Sho. 58-63486, the carriage is moved to the center of the recording sheet upon reception of a set of instructions; the recording sheet is forwarded to the print start position; and the carriage is returned to the original position to start printing when the operation of inserting the recording sheet has been completed.
In Unexamined Japanese Patent Publication No. Sho. 61-233569, the printer is arranged to move the carriage to the center of the recording sheet so that the carriage can guide the recording sheet while forwarding the recording wheet to the print start position upon operation of the sheet insertion button. Then, the operation of inserting the recording sheet has ended. After that, the operation of printing a single line is performed by moving the carriage along the recording sheet. When a single line printing is accomplished, the carriage is moved again to the center of the recording sheet. Then, a line feed operation is carried out. These steps of the printing, the carriage centering and line feeding are repeated until the top end of the recording sheet reaches the paper guide.
In Unexamined Japanese Patent Publication No. Sho. 61-263780, the recording sheet is forwarded by performing the line feed operation with the recording head moved to the center of the recording sheet from the print end position until several lines in the top margin of the recording sheet reach the guide section.
Based on the above printers, the cost of manufacturing may be reduced to such a degree as to permit, for example, a paper bail. However, because the line feed operation is still performed after the recording head is moved to the center of the recording sheet, the printing throughput is reduced in proportion to the time required for moving the carriage to the center. In addition, because a zone in the center of the recording head which is guided by the carriage is limited to the size of the carriage, the recording sheet is likely to be jammed.
Accordingly, it is desired to provide a printer which is capable of reliably introducing the top end of a recording sheet to the printer by increasing the guide zone in the center of the recording sheet, while improving the total print speed from sheet insertion to print end.